Magnetovolume coupling in transformation behaviour of Mn–Ni–Sn metamagnetic shape memory alloys

The shift rate of transformation temperature as a function of the magnetic field is one of the crucial parameters predetermining the promising functional properties originated from the martensitic transformation (MT) of the Heusler metamagnetic shape memory alloys (MetaMSMAs). In the present work, we interrelated such a shift of MT temperature with the volume magnetostriction constant and estimated this constant using the recent experimental data obtained for two Mn–Ni–Sn-based MetaMSMAs. As a consequence, the role of the magnetovolume coupling in the transformational behaviour of these two alloys and the nature of magnetic state inherent to their austenitic and martensitic phases have been revealed. It has been shown that the shift of MT temperature under the strong magnetic field and the magnetization jump accompanying MT can be caused by both the forced and spontaneous volume magnetostriction if magnetoelastic constant is large and positive. (paper)